1. Field of the Invention
The present invention relates to a diaphragm for loudspeakers. More specifically, the present invention relates to a diaphragm for loudspeakers, which is lighter in weight, and higher in performance in the use of a base material made of a material low in density and high in modulus of elasticity.
2. Description of the Prior Art
Generally it is considered ideal that the diaphragm for loudspeakers follows, with sufficient linearity, the driving force given by an electromagnetic conversion system within the working frequency zone, and the entire face thereof vibrated (piston vibration) at the same phase. A so-called flat diaphragm whose radiation face is flat is considered ideal in terms of sound-wave radiation characteristics. According to the flat diaphragm, to prevent split resonance from spreading the piston vibration range, the rigidity, which was due to the profile effect in a cam type or a dome type, was depended upon the thickness of the diaphragm. As a result, the weight of the diaphragm was increased, thus decreasing the performance of the loudspeaker. As a method of overcoming this defect, a diaphragm was used of a sandwich structure wherein a skin material was bonded on the surface of a hollow core base material. However, the light-weight effect was not sufficiently provided, even if the rigidity was enhanced to a certain degree, by the use of such a sandwich structure as described above. To further increase the light-weight effect, the material, which was used to make the sandwich structure, was made thinner to reduce the weight. However, the mechanical strength was reduced causing buckling, deformation during the assembling operation and partial resonance (face-flutter phenomenon) during the operation, thus deteriorating the acoustic characteristics.
To improve the weight defect in such a flat diaphragm as described above, a material, having a low density and a high modulus of elasticity is desired. Aluminum or titanium was chiefly used as the general material for an acoustic transducer. Also, in the diaphragm of such sandwich structure as described above, the balance between the properties of the matter used for the skin material and the base material was important. When a skin material of beryllium, boron or the like was combined with a base material of aluminum, the degree of contribution towards the characteristics of the diaphragm due to the property of the matter was lower as compared with the case where aluminum or titanium was used as the skin material. Thus, it has been difficult to sufficiently rely upon the property of the skin material. A honey-comb material, a ribbon braided material, etc. have been put in use as a base material of a hollow core of a diaphragm for a loudspeaker made as a sandwich structure. The honey-comb material had the disadvantage of a lower weight-decrease degree, because the cells become partially double. The ribbon braided material had the disadvantage in that the long ribbon had to be bent into a small diameter, thus effecting the working property of the material and complicating the braiding process, whereby the productivity became inferior.